This invention relates to a recording head positioning device for moving a recording head rotationally to a predetermined position over a recording medium.
Magnetic disk apparatus employ head positioning devices based on linear-drive voice coil motors (abbreviated by "VCMs") with the intention of fast and accurate head movement and positioning. The VCM comprises a coil disposed in a magnetic field which is produced in a space between fixed magnetic poles, and operates by being supplied with a current to the, coil. In recent years, magnetic disk apparatus have been required to be compact in size and fast in access operation, and therefore compactness and large output are crucial for the VCM. In order to meet the demand, various improvements have been made on the VCM, which includes the use of high-performance magnets for reducing the size of the magnetic circuit, the use of a rectangular or flat wire for the coil conductor, the elimination of the bobbin for increasing the effective length of winding, and the use of a light-weight material and structure for the head and the carriage which supports the head for the movement. However, in the linear-motion actuator, the mass of its linear movement portion such as the carriage forms a direct load of motion, and therefore the accomplishment of a compact actuator is difficult. On this account, magnetic disk apparatus smaller than eight inches (about 20 cm) in disk diameter mostly employ rotary actuators.
A rotary actuator, as shown in FIG. 14, comprises a carriage 70 supported rotatably on a shaft 76 of a carriage support member 75, with a magnetic head 71 being mounted on one end and a coil 72 being wound on another end of the carriage 70. The distance of the coil 72 from the shaft 76, i.e., radial distance rc, is virtually equal to the distance rh of the magnetic head 71 from the shaft 76. A magnet 77 is fixed on the support member 75. The rotary actuator turns the carriage 70 to move the magnetic head 71 by producing a torque T which is expressed as a product of the electromagnetic force Fc created by the current flowing in the coil 72 and the radial distance rc of the coil. When the moment of inertia on the shaft 76 is assessed in terms of the equivalent mass at the head position, the carriage 70 which turns around the shaft 76 can have a smaller mass as compared with a linear actuator of the same size. Accordingly, the output required of the VCM decreases in proportion to the mass, and the reduction of size is possible.
Japanese Patent Unexamined Publication No. JP-A-57-191880 describes a head actuator intended for the above defect. This publication discloses the structure for fitting a motor at the end of the shaft of the carriage, but it describes nothing about the specific structure of the motor.
U.S. Pat. No. 4,398,167 discloses a specific structure of a motor which is fitted at the end of the shaft of the carriage. The motor is a moving-coil motor, in which a coil is fixed on the motor shaft and the coil section is adapted to turn.